Math 2.0

Manifolds and cell complexes Three-manifolds Example

Seifert–Weber space

Example

Take a solid regular dodecahedron. Glue each face to the opposite face after a turn of 3/103/10 of a full turn, that is, by the angle 3π/53\pi/5. The result is the Seifert–Weber space WW, a closed orientable 3-manifold.

Under these gluings, the 3030 edges of the dodecahedron fall into 66 classes of 55 edges, and all 2020 vertices become one point. The cell structure has 11 vertex, 66 edges, 66 faces and 11 cell. So its Euler characteristic is 1−6+6−1=01 - 6 + 6 - 1 = 0, as it must be for a closed 33-manifold. In hyperbolic space ℍ3\mathbb{H}^3 there is a regular dodecahedron with dihedral angles 2π/52\pi/5. With this dodecahedron the 55 angles around each edge class add up to 2π2\pi, and the gluing maps are isometries. So WW is a closed hyperbolic 3-manifold.

Remarks

Its first homology group is (ℤ/5)3(\Z/5)^3. Gluing opposite faces with a turn of 1/101/10 instead gives the Poincaré homology sphere, and a turn of 1/21/2 gives the real projective space ℝℙ3\mathbb{RP}^3. Seifert and Weber described the space in 1933; it was one of the first known closed hyperbolic 33-manifolds.

Further reading

  1. Web https://en.wikipedia.org/wiki/Seifert%E2%80%93Weber_space
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Changed2 November 2026

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